I noticed that almost all email messages I get do not embed images, but link them from the http instead (and they get blocked by default of course). I'm sending HTML email for my service and can easily embed images to create better visual experience. Is there particular reason not do so? Why everybody else is linking instead of embedding?
Because by embedding the images in the email, the email size gets a lot larger, uses more bandwidth for you to send it, and more for them to receive it. If the images are important to the email's purpose then embed them, if they are to just make it look good then link them.